The present invention relates to an arrangement for selectively connecting gear wheels mounted for rotation about a common axis and incorporated in a gear train in general, and more particularly to such an arrangement as used in a printing machine selectively operable in a first page printing mode and a first and second page printing mode.
In printing machines which are capable of operating in the first and second page printing mode, that is, in printing machines including a plurality of printing stations of which at least one prints on one side of the respective sheet while at least one other prints on the other side of the same sheet, it is conventional to so transfer the respective sheet from a preceding printing roller to a succeeding sheet transfer roller that the sheet is gripped at a tangential region at its then trailing edge portion. Then, the sheet is transferred on this sheet transfer roller to another gripping system to be thereafter transported with its previously trailing edge portion ahead. On the other hand, when it is desired to print images at consecutive printing stations only on one side of the sheet, the sheet is transferred at a corresponding tangential region from the previous printing roller to the sheet transfer roller in such a manner that it is gripped at its leading edge portion and then transported in this orientation. In order to render it possible for the suction devices or for the mechanical gripping devices of the sheet transfer roller of a printing machine which is convertible for operation either in the first page printing mode or in the first and second page printing mode to engage the respective sheet at its leading edge portion in one instance and at its trailing edge portion in the other instance, it is necessary to provide for the necessary positional or phase adjustment in the printing machine either upstream of or downstream of the sheet transfer roller.
In the German Democratic Republic patent No. 135,812, there is disclosed an arrangement in which the printing stations are driven by gear wheels which form a continuous gear train. The adjustment of the printing machine between the two above-discussed printing modes is rendered possible by the incorporation of a double gear wheel in the gear train. Herein, the double gear wheel is so constructed that a first of these gear wheels is rigidly connected with the respective cylinder or roller of the printing machine, while the other is pressed by a spring force against the first gear wheel, so that there is obtained a force-transmitting engagement between the two gear wheels which results in entrainment of the other gear wheel for joint rotation with the first gear wheel. This force-transmitting engagement can be terminated or temporarily discontinued when it is desired to change the relative angular position of the other gear wheel with respect to the first gear wheel by operating centrally operatable screws.
In the prior-art arrangement of this type, the adjustment of the drive is considerably improved as compared to the situation existing prior to this construction. Even planarly acting pressing forces are constantly reproducible after each adjustment of the drive. However, what is disadvantageous in this construction is that the lid or panel which completes the respective lateral wall must be removed before, and replaced after, each adjustment. A considerable time expenditure is involved in this quite laborious operation and, in addition thereto, the time needed for removing and replacing this paneling or cladding increases the idle time of the printing machine during the adjustment.